Question: Our school library started the day with $284$ books. During the day, $28$ books were returned, and some others were checked out. At the end of the day, the school library had $293$ books. How many books were checked out today?
Answer: $\text{Not checked out}$ $\text{Checked out}$ ${?}$ $293$ $284+28$ If no books were checked out, the library would have $284+28=312$ books at the end of the day. $312-293=19$ ${19}$ books were checked out.